At the center of Öskjuhlíð, a hill planted with more than 176,000 trees, is the spectacular glass dome of the Pearl. This stunning feat of architecture can carry up to a million gallons of geothermal water—the lifeblood of the city's energy supply—and also houses a revolving restaurant, café and observation platform. Outside, gentle trails have views of the city and nearby Nauthólsvík (Nauthólsvegi, 101 Reykjavík), an otherworldly beach where you can bathe in warm geothermal waters.